The present invention relates to a method of and apparatus for processing scroll members of scroll type fluid machines which are used as compressors or expanders for gases such as air, refrigerant and so forth.
The scroll type compressor is disclosed, for example, in U.S. Pat. No. 4,065,279, wherein a stationary scroll member and an orbital scroll member assembled together, with the orbital scroll member being driven to make an orbital movement with respect to the stationary scroll member to progressively decrease the volume of fluid chamber to thereby compress and discharge the fluid.
In the scroll type fluid machines of the aforementioned type, the stationary and orbital scroll members have respective spiral wraps the walls of which make contact with each other so as to define a closed space serving as the working fluid chamber. The point of contact between the spiral wrap walls of the scroll members, sealing the working fluid chamber, is gradually changed to progressively decrease the volume of the chamber to raise the pressure of the fluid in the chamber. It is, therefore, essential that the side walls of the spiral wraps and contact surfaces of the end plates of the scroll members are finely finished.
To cope with this demand, fine surface finishing or processing has been accomplished by an end mill cutter. In the final processing of the spiral wrap surfaces with an end mill cutter, it is necessary to move the cutter relatively to the wrap along the involute form of the latter, from the center to the periphery and vice versa. This method inconveniently necessitates independent processings for the inner and outer surfaces of the wrap, requiring much time and labor. Thus, the final processing with end mill cutter is not suitable for the mass production of the scroll members and, cannot assure satisfactory finishing particularly on the side surfaces of the wraps.
As means for eliminating the above-described problems of the prior art, Japanese Patent Laid-Open No. 149030/1982, corresponding to U.S. patent application Ser. No. 239,414, proposes a processing method in which a broaching tool, having a cutting edge of the same shape as the involute form of the stationary or orbital scroll member, is moved in the axial direction of the scroll member along the side surface of the latter to effect the final processing. It will be clear to those skilled in the art that this method can considerably shorten the processing time as compared with the conventional method which employs the end mill cutter. When each side wall of a wrap is processed independently by this processing method, however, the cutting edge of the broaching tool is made to contact with the wrap side wall while making angular indexing for several times until the desired size and state of finish is attained. For effecting the broaching on both side walls simultaneously, it is necessary to use a series of broaches. Thus, this method still requires an impractical long time. For processing the wraps having involute forms.
A considerably large resistance will be encountered during simultaneous processing on both side walls of a wrap by tools having cutting edges of the same involute forms as the wrap side surfaces. The large resistance inevitably requires a large pressing force which, in turn, requires a larger size of the pressurizing apparatus. In order to conduct the processing with minimum pressurizing force on the cutting edges, it is advisable to increase the number of cutting cycles while decreasing the amount of material removed in each cutting cycle. Such measure, however, is not preferred from the view point of shortening of the processing time. In addition, an increased processing time inconveniently shortens the life of the cutting tool. In fact, it is not possible to finish the wrap side surface at a sufficiently high precision with a cutting tool after a long use. In order to achieve sufficiently high precision of the finished surfaces with a single tool for a number of scroll members, it is necessary to prolong the life of the tool by shortening the processing time while reducing the amount of material removed and, at the same time, decreasing the required cutting pressure.